This invention relates to rotary fluid displacement apparatus, and in particular, to fluid compressor units of the scroll type.
Scroll-type apparatus have been well known in the prior art as disclosed in, for example, U.S. Pat. No. 801,182, which discloses two scroll members each having an end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between spiral curved surfaces to thereby seal off and define at least one pair of fluid pockets. The relative orbital motion of the scroll members shifts the line contact along the spiral curved surfaces and, therefore, the fluid pockets change in volume. The volume of the fluid pockets increases or decreases depending on the direction of orbital motion. Therefore, the scroll-type apparatus is applicable to compress, expand or pump fluids. When the scroll-type apparatus operates as a compressor, the fluid pocket moves to the center with a reduction of pocket volume by the relative orbital motion of the scroll members, to thereby compress the fluid in the pocket. Sealing at the line contacts of the spiral elements must be maintained if the apparatus is to function efficiently.
Each of the scroll members may be supported on a crank pin disposed at the end surface of a drive shaft for imparting relative orbital motion to both scroll members. That is, the scroll members are cantilevered. However, imbalance due to the orbiting motion of the scroll members causes the drive shafts and the scroll members to undergo axial slant, disrupting the line contact of both spiral elements.
In order to minimize this undesirable condition, one of the scroll members is fixedly attached to the compressor housing, while the other scroll member is supported on the crank pin of a drive shaft. However, the movement of the orbiting scroll member is eccentric with respect to the axis of rotation of the driveshaft, and axial slant may still easily occur. This leads to disruption of the line contact between the spirals increased vibration of the compressor during operation, and noise due to striking of the spiral elements.
In order to minimize axial slant, a supporting mechanism, such as a thrust bearing, has been devised for supporting the orbiting scroll member. An axial thrust force on the orbiting scroll member is produced by compressed fluid in the fluid pockets. Therefore, the orbiting scroll member is pushed against the thrust support mechanism to minimize axial slant. However, maximum thrust force is produced only during steady state operation. When the apparatus is not operating, the thrust force is not present. Hence, axial slant will occur during start-up and shut-down, when the thrust force is nonexistent or insufficient to press the orbiting scroll member against the thrust support mechanism. When an antifriction bearing is employed as the thrust support mechanism, fretting of the bearing and noise are caused by the axial slant.